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%I #10 Aug 22 2017 20:53:11
%S 1,2,3,6,6,22,16,66,83,300,296,2243,1778,9780,20640,58428,79554,
%T 600798,567544,3671978,6935746,23785912,31017008,246156513,282456333,
%U 1357927400,2615206733,11358512518
%N Number of step cyclic shifted sequence structures using a maximum of three different symbols.
%C See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. Permuting the symbols will not change the structure.
%D M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]
%F Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
%F a(n) = Sum_{k=1..3} A288627(n, k). - _Andrew Howroyd_, Jun 13 2017
%Y Cf. A056411, A288627.
%K nonn
%O 1,2
%A _Marks R. Nester_
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